Rivet analyses

Charged particle multiplicity and 2nd Fox-Wolfram moment in χb0, 1, 2′ Decays

Experiment: CLEOII (CUSB)

Inspire ID: 32611

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D46 (1992) 4822-4827

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_b(2P), original e+e-> Upsilon(3S)

Measurement of the average charged particle multiplicity, and the charged multiplicity distribution in χb0, 1, 2′ Decays. In addition the average 2nd Fox-Wolfram moment, and its distribution is also measured.

Source code:CLEOII_1992_I32611.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief chi_b(2S) decays
  class CLEOII_1992_I32611 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1992_I32611);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(),"UFS");
      // Book histograms
      // averages
      book(_h_N_aver ,1,1,1);
      book(_h_R2_aver,1,1,2);
      // dists
      _h_N  = {Histo1DPtr(),Histo1DPtr(),Histo1DPtr()};
      _h_R2 = {Histo1DPtr(),Histo1DPtr(),Histo1DPtr()};
      book(_h_N [0],2,1,1);
      book(_h_N [1],2,1,2);
      book(_h_N [2],2,1,3);
      book(_h_R2[0],3,1,1);
      book(_h_R2[1],3,1,2);
      book(_h_R2[2],3,1,3);
    }

    void findDecayProducts(Particle parent, Particles & children, unsigned int & nCharged) {
      for(const Particle & p: parent.children()) {
    if(p.children().empty()) {
      if(isCharged(p)) ++nCharged;
      children.push_back(p);
    }
    else
      findDecayProducts(p,children,nCharged);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles chib = apply<UnstableParticles>(event,"UFS").particles(Cuts::pid==110551 or
                                       Cuts::pid==120553 or
                                       Cuts::pid==100555);
      for(const Particle & p : chib) {
    unsigned int iHist = (p.pid()%10)/2;
    unsigned int nCharged(0);
    Particles children;
    findDecayProducts(p,children,nCharged);
    // ncharged
    _h_N     [iHist]->fill(nCharged);
    _h_N_aver->fill(iHist,nCharged);
    // R_2
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    vector<FourMomentum> mom;
    mom.reserve(children.size());
    for(const Particle & p2: children) {
      mom.push_back(boost.transform(p2.momentum()));
    }
    // compute R2
    double H0(0.),H2(0.);
    for(const FourMomentum & p1:mom) {
      double mod1 = p1.p3().mod();
      Vector3 axis = p1.p3().unit();
      for(const FourMomentum & p2:mom) {
        double mod2 = p2.p3().mod();
        double cTheta = axis.dot(p2.p3().unit());
        H0 += mod1*mod2;
        H2 += mod1*mod2*0.5*(3.*sqr(cTheta)-1.);
      }
    }
    double R2=H2/H0;
    _h_R2     [iHist]->fill(R2);
    _h_R2_aver->fill(iHist,R2);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<3;++ix) {
    normalize( _h_N [ix]);
    normalize( _h_R2[ix]);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    vector<Histo1DPtr> _h_N,_h_R2;
    BinnedProfilePtr<int> _h_N_aver,_h_R2_aver;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CLEOII_1992_I32611);

}